Pulse width modulation (PWM) signals often are used for precise control of electronic devices, such as electric motors, light emitting diode (LED) backlights, and the like. In some systems, an input PWM signal is used to generate multiple PWM signals in parallel, and the multiple PWM signals are then used to drive one or more respective components. In generating multiple output PWM signals, it often is advantageous to synchronize the output PWM signals with the input PWM signal. To illustrate, in display systems implementing LEDs controlled by the output PWM signals, the input PWM signal often is synchronized with the display frame frequency, so a lack of synchronization between the output PWM signals and the input PWM signal can result in visual noise due to beating between the display frame frequency, the output PWM frequency, and their harmonics. Further, it can be advantageous to phase-shift the parallel output PWM signals in relation to each other to avoid or reduce undesirable effects, such as increased electromagnetic interference (EMI), large ripple in the power supply voltage when the components driven by the multiple PWM signals share the same power supply, and audible noise when the output PWM signals have a frequency in the human audible range.
For video-based systems, one conventional approach involves the direct use of the input PWM signal to drive multiple parallel strings of LEDs of a display in instances whereby the input PWM signal is synchronized to the frame rate of the display. However, the input PWM signal typically has a relatively low frequency and this approach therefore often has a number of undesirable ramifications, such as the introduction of audible noise and relatively large voltage ripple in the voltage supply, and increased power consumption. In other conventional systems, a frequency converter is used to convert the input PWM signal to a higher-frequency PWM signal that is then used to directly drive the parallel LED strings. However, this approach often results in the loss of synchronization between the PWM signal and the frame rate and thus is susceptible to visual noise issues, such beating between the frame rate, the frequency of the converted PWM signal, and their harmonics. Accordingly, other conventional approaches have sought to avoid these issues through the use of a phase-locked loop (PLL). However, the frequency of the input PWM signal and the frame rate often can be relatively low, thus requiring the use of a PLL with a low reference frequency and a small loop bandwidth. Such PLLs typically have a long locking time and require a relatively large area for implementation, thereby adding considerable cost and complexity to any design implementing a PLL-based solution.